Auditory processing disorder (APD), a poorly defined and understood listening difficulty, is diagnosed in about 50,000 children in the US annually. The primary goal of this research is to increase understanding of APD and to provide more rational diagnosis and better management of children with listening difficulties. There are two major theories of APD, that it is a problem with `bottom-up' processing of sounds by the central auditory nervous system (CANS) or, alternately, that it is due to `top-down', more general cognitive difficulties resulting in impaired attention, working memory and executive function. The proposed research will examine these theories in detail in children aged 6-12 years attending clinics at Cincinnati Children's Hospital because of suspected listening difficulty (LiD), but with clinically normal hearing thresholds. Children will be screened using a novel, well-validated, caregiver questionnaire (the ECLiPS) specifically designed to identify LiD in everyday life. Specific hypotheses are that, (i) current clinical methods to diagnose APD do not distinguish between bottom-up and top-down impairments, (ii) children with LiD have impaired speech-in-noise and spatial processing due to impaired, bottom-up auditory function deriving from the ear or the CANS, and (iii) children with LiD have impaired auditory cognition, reflected in auditory attention, working memory and executive function and their biological correlates in the cerebral cortex. The study will be novel through its use of a wide variety of sensitive, cutting-edge behavioral and physiological approaches that specifically address these hypotheses. Baseline data will be collected from 6-9 year olds in three demographically matched groups (each n=50) who are typically developing (TD), or who have LiD with (AP+) or without (AP-) a clinical diagnosis of APD. Quantitative modeling of data in a longitudinal design will be used to establish maturational trajectories for each group and the individuals within them. It is predicted that most children with LiD will have a variety of both CANS and cognitive dysfunction, but that some distinct profiles will emerge. Based on our previous research and on clinical reports, we expect that most children with LiD will have a generalized cognitive deficit that is common to a variety of language-based learning difficulties. However, we also expect to find some children who have identifiable disorders (e.g. of the inner hair cell afferent synapse, brainstem conduction speed, or cortical white matter integrity) underlying impaired ability of the ear, CANS or cortex to generate, integrate or transmit supra-threshold, time-sensitive signals. Our methods will enable us to localize the source of those disorders. The data obtained from this study will have immediate impact on the diagnosis of APD, with implications for differential management, dependent on the specific nature of the problems identified. They will also provide novel information on the normal, integrated function and development of the human auditory system, with implications for other sensorimotor systems, human development, learning and learning disorders.